This invention relates to a filtration system for a solvent-spun fibre manufacturing process and plant.
In the manufacture of solvent-spun fibres such as, for example, Tencel cellulose fibres (Tencel is a trade mark of Courtaulds Fibres Limited), a dope comprising an aqueous solution of woodpulp and amine oxide, is supplied under pressure to a spinning head. The spinning head comprise a plurality of spinnerette jets which are typically 80.mu. or less in diameter. The dope is extruded through the spinnerette jets into a spin bath where the solvent is leached out of the fibre and the fibre is washed by water. The fibres are collected, washed and dried whilst the waste aqueous amine oxide solution is recovered and returned to the process.
The spinnerette jets are typically of the order of 80.mu. diameter and are carefully shaped and designed to optimise fibre production. In a modern fibre production plant, there can be as many as 200 spinning heads with up to six spinnerette plates each of which could have as many as 7,000 jet holes of 80.mu. diameter. It is therefore essential to filter out particles or lumps in the dope which could block the spinnerette jet holes. The most obvious way to do this is to provide a series of filters of decreasing mesh sizes with the first filter of the series having the coarsest mesh and the downstream most filter, immediately in front of the spinnerette jets, having the smallest mesh size (less size than the diameter of the spinnerette jet). The finer the mesh, the more efficient will be the filter and the more likely it is to block up rapidly.
It has been found to be impractical to achieve satisfactory filtration of the dope when using a series of filters arranged with decreasing mesh sizes because the finest filter immediately upstream of the filter blocks up easily and requires frequent changing and cleaning.
Furthermore, because of the large number of filters that would be required upstream of the spinning heads, (one for each spinning head), and the need to change them frequently, if they were to be of much smaller mesh than the diameter of the jets (80.mu.) it would be impossible to achieve a satisfactory design of filter, which is easy to clean.
An object of the present invention is to provide a filtration system for a solvent-spun fibre manufacturing process which comprises a plurality of sets of filters in flow series and which are easy to clean without disrupting the flow of dope to the spinning heads of the process plant.